How to get posts by using Ajax tab?

I’m trying to create tabs in WordPress theme, and those tabs having a tab for last comments and another tab for getting posts from a specific category that i have in my blog.
and i want to use Ajax tab so the content doesn’t loading till the user click on it that tab.
the problem is those Ajax using an external pages, so how can i add code to get posts in external page inside the theme folder.

Hope anyone can help